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The giant fossil dragonflies are likely a completely different genus and species of modern dragonflies; I doubt any number of generations would produce a 30cm long dragonfly out of modern animals.

CJSF

"A scientific theory
Isn't just a hunch or guess
It's more like a question
That's been put through a lot of tests
And when a theory emerges
Consistent with the facts
The proof is with science
The truth is with science"-They Might Be Giants, "Science Is Real"lonelybirder.org

In addition to the higher O2, would the higher CO2 in the past have facilitated giantism?

It's interesting that both have been at higher levels. When we state higher levels, we are actually stating a higher level proportionally, not necessarily that there was a greater amount overall in the atmosphere at the time.

I think it fair to state the following as a general principle: spread the same amount of a substance over a greater area, it will be appear reduced in any particular area, but still be the same amount overall.

Yes, Clarke is correct. As he says, larger organisms need different proportions from smaller organisms.

Grant Hutchison

I can see that a mouse the size of an elephant would need the proportions of an elephant, or its legs would break...but what about visa versa? Could an elephant the size of a mouse work? Its legs would certainly be strong enough.

I can see that a mouse the size of an elephant would need the proportions of an elephant, or its legs would break...but what about visa versa? Could an elephant the size of a mouse work? Its legs would certainly be strong enough.

Over evolutionary periods, probably not. IMO its proportions would change radically in a few generations as it adapted to its new size.

There's no such thing as a shrink-ray, so the reduced size would mean reduced numbers of cells in the brain, muscles, organs. So maybe the elephant would not have the same leg strength. Maybe its bones would be brittle. It's brain certainly would not operate the same way. Maybe some organs might be too proportionately small compared to the body to keep it alive long.

Or maybe not, I haven't performed that experiment yet.

"I'm planning to live forever. So far, that's working perfectly." Steven Wright

I can see that a mouse the size of an elephant would need the proportions of an elephant, or its legs would break...but what about visa versa? Could an elephant the size of a mouse work? Its legs would certainly be strong enough.

Its legs would be fine, but it would have other surface area/volume problems. Its surface area would be larger in proportion to its metabolizing tissue mass, so it would lose heat more readily. (It's not a coincidence that small mammals generally have more insulating fur than large mammals.) So it would need a higher metabolic rate (per mass) to maintain body temperature. Even if it could ramp up metabolism to the required level, it would need to eat more food to fuel that - and elephants are adapted to a high-volume, low energy-density diet, so might have trouble ingesting enough in the time available. It might also have trouble finding plant food that matched its foraging adaptations - they're designed to rip chunks of foliage off and grind them, not to climb around and nibble bits off plants that are large and rubust in comparison to their own body mass.
Dead in a day, I'd say.

My educated guess is that if we could create a mouse with leg bone thickness proportional to that of an elephant, it would be less agile when trying to escape from predators, and thus would be at an evolutionary disadvantage.

The giant fossil dragonflies are likely a completely different genus and species of modern dragonflies; I doubt any number of generations would produce a 30cm long dragonfly out of modern animals.

CJSF

Not even dragonflies. Griffinflies, if you want to use their "real names".

While most certainly an ancestor, griffinflies lack the specific identifying features that make dragonflies dragonflies. If you took a mayfly and squished it between two rocks for 250 million years I'm sure a layman would think it was a dragonfly.

Though they had already evolved the larval flip-out lower labium common to the group.

Time wasted having fun is not time wasted - Lennon
(John, not the other one.)

Its legs would be fine, but it would have other surface area/volume problems. Its surface area would be larger in proportion to its metabolizing tissue mass, so it would lose heat more readily. (It's not a coincidence that small mammals generally have more insulating fur than large mammals.) So it would need a higher metabolic rate (per mass) to maintain body temperature. Even if it could ramp up metabolism to the required level, it would need to eat more food to fuel that - and elephants are adapted to a high-volume, low energy-density diet, so might have trouble ingesting enough in the time available. It might also have trouble finding plant food that matched its foraging adaptations - they're designed to rip chunks of foliage off and grind them, not to climb around and nibble bits off plants that are large and rubust in comparison to their own body mass.
Dead in a day, I'd say.

Grant Hutchison

Depends. Outside it would get eaten before anything else had a chance to happen.

Inside I would keep it warm and start it on a grain based diet for the carbs and fat.

I'm a former small critter guy if you may recall.

Elephants used for labor are fed a high calorie doughy "bread" so they don't have to browse all day.

Time wasted having fun is not time wasted - Lennon
(John, not the other one.)

Originally Posted by Tom Mazanec
I can see that a mouse the size of an elephant would need the proportions of an elephant, or its legs would break...but what about visa versa? Could an elephant the size of a mouse work? Its legs would certainly be strong enough.

Its legs would be fine, but it would have other surface area/volume problems. Its surface area would be larger in proportion to its metabolizing tissue mass, so it would lose heat more readily. (It's not a coincidence that small mammals generally have more insulating fur than large mammals.) So it would need a higher metabolic rate (per mass) to maintain body temperature. Even if it could ramp up metabolism to the required level, it would need to eat more food to fuel that - and elephants are adapted to a high-volume, low energy-density diet, so might have trouble ingesting enough in the time available. It might also have trouble finding plant food that matched its foraging adaptations - they're designed to rip chunks of foliage off and grind them, not to climb around and nibble bits off plants that are large and rubust in comparison to their own body mass.
Dead in a day, I'd say.

Grant Hutchison

So, in other words, if you made an elephant as small as a mouse, you would have to make other adaptions for that small size (more fur, higher metabolic rate, eat more food, adopt to a diet to meet those requirements), and you would essentially have: a mouse!

So mice are not arbitrarily mouse-like, and elephants are not arbitrarily elephant-like, but are adapted to live in the environment where they live. Gee, almost sounds like those characteristics evolved that way.

Interestingly, baby elephants are quite hairy, though I'm not convinced they're hairy enough to produce useful insulation. I think they probably reduce their heat loss by staying under the rest of the herd - a sky that consists mainly of elephant is a lot warmer than the open sky on a cold day.
(I once had my hand sucked by a baby elephant. It felt like the fingernails might actually lift off - these little fellas are strong.)

So, in other words, if you made an elephant as small as a mouse, you would have to make other adaptions for that small size (more fur, higher metabolic rate, eat more food, adopt to a diet to meet those requirements), and you would essentially have: a mouse!

So mice are not arbitrarily mouse-like, and elephants are not arbitrarily elephant-like, but are adapted to live in the environment where they live. Gee, almost sounds like those characteristics evolved that way.

I also find it amusing to imagine locomotion in a mouse-sized elephant. Elephants don't need to move at great speed to escape predators. Mice do. Even if elephants were to be so small, with biomechanics being what they are I picture them as still "lumbering" which strikes me as comical. So there we have it: a starving, hypothermic, lilliputian elephant that's sure to be snagged by house cat an minute now and without any real effort.

Walking would probably be tricky, because they'd find themselves leaving the ground with each step, being overpowered for their mass. And they'd be able to jump several times their own height, with no idea how to land right way up.

"By altering her designs, Nature can circumvent to a quite remarkable degree the limitations imposed by changes of scale. Consider for example the difference between the albatross and the tiniest midge, barely visible to the eye. Both are aerial creatures, both fly by flapping their wings - and there the resemblance ceases. Anyone knowing only the midge could make a very convincing case for the impossibility of the albatross - and vice versa. Yet both exist and both fly, though one weighs a billion times as much as the other. No bird much larger than the albatross could fly....no insect much smaller than a midge could have any control of it movements through the air." (Arthur C Clarke)

Theoretically, on an earth-like planet 20% less massive, with 20% less gravity, could a straight-scaled up population of 7'-9' humans be feasible?

No. There are other variables like O2 content that need to be addressed.

I think that with an increase of that ratio, the oxygen content would still be OK, though maybe it would depend on where in the range you are talking about. After all, there have been people more than eight feet tall who have lived fairly long lives, and I think the problems they experienced were mainly due to skeletal problems rather than being able to get enough oxygen. But I think the tallest man ever was almost nine feet tall.

I think that with an increase of that ratio, the oxygen content would still be OK, though maybe it would depend on where in the range you are talking about. After all, there have been people more than eight feet tall who have lived fairly long lives, and I think the problems they experienced were mainly due to skeletal problems rather than being able to get enough oxygen. But I think the tallest man ever was almost nine feet tall.

But not proportioned like a 5' 10'' man. (IE "scaled up")

ADDED: Lung and heart size would need to be adjusted accordingly. Giants may have heart problems because of their body volume.

Last edited by Noclevername; 2017-Mar-15 at 12:31 AM.

"I'm planning to live forever. So far, that's working perfectly." Steven Wright

ADDED: Lung and heart size would need to be adjusted accordingly. Giants may have heart problems because of their body volume.

I see, we are talking about different things. I was only talking about whether they could survive, you meant if they could survive without any health problems. The answers will obviously be slightly different.

Well, it would reduce gravity by 20% if you managed to have a planet that was less massive, but exactly the same radius (which could be possible if the composition is different). In general, you'd need to know both the mass and the radius of the planet to be able to determine the surface gravity.

They article I read mentioned .6 g surface gravity for an inflated Mars.

I didn't include it as I wasn't sure it was correct.

Given the surface gravity of Mars is about 0.38g now, that was bound to be incorrect - it has to go down rather than up when "inflated".
Surface gravity scales directly with mass and inversely with radius squared. So if the radius is the same as Earth, but the mass is the same as Mars (0.1 Earth), then the gravity would be 0.1 of Earth.

Ah. But if you mean that Mars stayed the same density while being expanded, then its volume increases 6.6 times, therefore 6.6 times the mass, so this version of Mars is 0.66 time the mass of Earth and has 0.66 times the gravity.

Grant Hutchison

Last edited by grant hutchison; 2017-Aug-09 at 12:28 PM.
Reason: Last para

"For the human body is a piece of architecture that has evolved to give its best performance when it is 5 or 6 feet tall. Double its height and it would weigh eight times as much; but the bones which supported it would be increased in area of cross section only four times. The stresses acting upon them would therefore be doubled in intensity; a 12 foot giant is possible, but he would always be breaking his bones and he would have to be careful how he moved. To make a 12 foot version of homo sapiens practical would involve a major redesign, not a straight scaling up.The legs would have to be proportionately much thicker, as the example of the elephant shows. The horse and the elephant both follow the same basic quadripedal design - but compare the relative thickness of their legs! The elephant must be near the sensible limit of size for a land animal."

Is Clarke correct, in view of the fact that the fossil record shows that x5-x10 larger than today flora and fauna existed in the past: mosses which once grew up to 3 feet tall now reach only 1", cockroaches 12" now 1", shellfish 5 feet across now 8", crocodiles could reach 50 feet in length, today a paltry 12 feet, dragonflies with 4 foot wingspans, now only 4" etc?

Clarke is noticing the same thing Galileo noticed centuries earlier: the square-cube law.

One other limit on some of these animals' sizes, such as lobsters, is overfishing, preferentially killing larger specimens. Leaving that aside, Clarke should have known about the fossil evidence of large mammalian herbivores, such as indricotherium, which had a mass approaching thirty tons. When he wrote Profiles of the Future-- the essays date from the late 1950s and early 1960s -- paleontological consensus was that large sauropods, like apatosaurus, were semi-aquatic, not strictly terrestrial.

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